Methods of forming high aspect ratio plated through holes and high precision stub removal in a printed circuit board

Abstract

The present invention relates to printed circuit boards (PCBs), and more particularly, to methods of forming high aspect ratio through holes and high precision stub removal in a printed circuit board (PCB). The high precision stub removal processes may be utilized in removing long stubs and short stubs. In the methods, multiple holes of varying diameter and depth are drilled from an upper and/or lower surface of the printed circuit board utilizing drills of different diameters.

The invention claimed is: 
     
       1. A method for forming a plated through hole in a printed circuit board having a second layer on top of a first layer where a target layer connects the second layer to the first layer, the method comprising:
 drilling a first hole having a first diameter a first predetermined depth into an upper surface of the printed circuit board through the second layer past the target layer and into an upper portion of the first layer; 
 drilling a second hole having a second diameter through the first hole to a bottom surface of the printed circuit board, the second hole extending from the upper portion of the first layer to the bottom surface of the printed circuit board; 
 plating the first hole and the second hole with a conductive material; and 
 drilling a third hole having a third diameter from the upper surface downwardly through the first hole and the second hole, where the third diameter is smaller than the first diameter and larger than the second diameter. 
 
     
     
       2. The method of  claim 1 , wherein the printed circuit board includes a plurality of plated through holes formed therein using the first hole, the second hole and the third hole in combination as produced in the method of  claim 1 . 
     
     
       3. The method of  claim 1 , wherein the first hole is drilled a predetermined depth; and wherein the predetermined depth is shorter than half the vertical distance of the printed circuit board. 
     
     
       4. The method of  claim 3 , wherein the third hole is drilled from the upper surface to a lower surface of the printed circuit board, the lower surface of the printed circuit board opposing the upper surface of the printed circuit board. 
     
     
       5. The method of  claim 1 , wherein the second diameter is smaller than the first diameter. 
     
     
       6. The method of  claim 5 , further comprising adding copper to other conductive surfaces on the printed circuit board by electrolytic plating. 
     
     
       7. The method of  claim 5 , further comprising adding copper to other conductive surfaces on the printed circuit board by electrolytic plating. 
     
     
       8. The method of  claim 1 , further comprising:
 embedding a first conductive material in the printed circuit board. 
 
     
     
       9. A method for forming a plated through hole in a printed circuit board having a first surface and an opposing second surface, comprising:
 embedding a first conductive material in the printed circuit board; 
 drilling a first hole having a first diameter from the first surface of the printed circuit board downwardly to a first predetermined depth; 
 drilling a second hole having a second diameter from the first surface downwardly through the first hole to a second predetermined depth; 
 plating the first hole and the second hole with a second conductive material; and 
 drilling a third hole having a third diameter from the first surface downwardly through the first hole and the second hole. 
 
     
     
       10. The method of  claim 9 , wherein the printed circuit board has a plurality of plated through holes formed therein using the first hole, the second hole, and the third hole in combination as produced in the method of  claim 9 ; and wherein the first conductive material is copper. 
     
     
       11. The method of  claim 9 , wherein the first surface is an upper surface and the second surface is a lower surface;
 wherein the first predetermined depth is from the upper surface to the embedded first conductive material; 
 wherein the second predetermined depth is from the first surface to the second surface; wherein second diameter is smaller than the first diameter; and 
 wherein the third diameter is larger than the second diameter and smaller than the first diameter. 
 
     
     
       12. The method of  claim 9 , wherein the second diameter is smaller than the first diameter; and
 wherein the third diameter is smaller than the first diameter and larger than the second diameter. 
 
     
     
       13. The method of  claim 12 , further comprising adding copper to other conductive surfaces on the printed circuit board by electrolytic plating.